//2009/08/29 23:00:56
#include <iostream>
#include <string>
#include <vector>
#include <map>
#include <queue>
#include <sstream>
#include <algorithm>

using namespace std;

class MostCommonLetters
{
public:
    string listMostCommon(vector <string> text)
    {
        vector<int> v(26, 0);
        int mmax = 0;
        for (int i=0; i<text.size(); i++)
            for (int j=0; j<text[i].size(); j++)
                if (isalpha(text[i][j]))
                {
                    v[text[i][j] - 'a']++;
                    mmax = max(mmax, v[text[i][j] - 'a']);
                }
        string s;
        for (int i=0; i<v.size(); i++)
            if (v[i] == mmax)
                s += i+'a';
        return s;
    }
};
